Stability constants containing crown ethers

FIGURE 5.10 Assessment of stability constant (log K) values of the complexes of crown ethers and their acyclic analogs with K+in methanol.25-77 Linear correlations between predicted and experimental log K values for the test set (a) of crown ethers and for the set of acyclic ligands (b) in Figure 5.6a. As QSPR models were built on the training set containing exclusively crown ethers, it is not surprising that predictions for the test set (a) are more reliable. 

The stability constants of the 1 1 alkali metal picrate complexes of diketone 18. heptacyclic terpyridyl 27 and flexible terpyridine 28 were estimated by hquid-liquid extraction, and the resulting log fj values for Na" " and are also given in Fig. 4. The affinities of 18 and 27 for these alkali metals are remarkably high for hosts containing only five or three ligand atoms, respectively. In water-saturated chloroform, pentadentate host 18 binds Na" and K more strongly than do most crown ethers. Compared to naphtho-18-crown-6 (26), 18 binds Na " 4000 times better, and K 40 times better. Even tridentate host 27 extracts alkali metal picrates into chloroform, whereas flexible model system 28 is ineffective under the same experimental conditions. The potent complexation... 

Related to this, a crown-ether containing nickel(II) bis(dithiocarbamate) complex 353 has been prepared (1471). As a multisite system, it is capable of exhibiting cooperative complexation of anion-cation pairs. Thus, a sixfold enhancement of the stability constant for acetate results when potassium is cobound at the crown-ether moiety in 353. 

A study of the selectivity of lariat aza[15] crown-5 (3.133) and BiBLE (bi-brachial lariat ether) diaza[18] crown-6 derived ligands (3.134) containing variously substituted arene rings showed that the Ag+ complex stability decreased as a function of the electron-withdrawing ability of the substituents, R, as measured by the substituents Taft o° inductive constant (a parameter measuring the electron-withdrawing... 

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